Ink jet printing systems create printed images by ejecting drops of ink from one or multiple printheads onto a media. Typically the printheads are positioned above the media leaving a small gap. The size of the gap may vary between different printing systems, but is typically in the range of one or several millimeters.
Due to the size of the gap it is important that media being printed on be as flat as possible. Variations in the height of the gap, for example caused by wrinkles, bubbles, etc., in the media may lead to print quality issues. If the printheads contact the media damage to the media, the printhead, or both, may occur.
In large format printers, such as so-called industrial printers, media may be in the form of large sheets of flexible or semi-rigid substrates, such as cardboard and vinyl. In such printers substrate sheets are often supported on a substrate support bed or table that uses a vacuum to hold the substrate securely against the substrate support bed. Use of vacuum systems is useful in preventing a substrate from moving during a printing operation, especially in printers where the substrate support bed is moved relative to the printer's printheads. Vacuum systems also help hold substrates flat against the substrate support bed.
However, despite the use of vacuum systems it is common, especially when using certain types of substrate, that air bubbles exist between the substrate and the substrate support bed. Such air bubbles prevent the media from lying flat against the substrate support bed, leading to height variations between the media and the printhead. Accordingly, print quality issues, or even damage to printer components, may occur.